1999 Mountaineer “Miss Fire” without codes. Not your typical question.

[Kage.]

I stuck this post here as I think I am out of the realm of the “Stock” portion of this forum:

I’ve got the build listed on my website (MidwestNomads) and over on Pirate 4x4 if you want the full on details of the build.

In a nutshell, the motor is the only part that hasn’t been touched during the build (185k mile 5.0). From the 5 gear swap on out, everything else has been touched. At this point I don’t know if the 5 gear swap might have caused part of the issue, but I kind of doubt it.

The issue I have been fighting pretty much since the inception of this build is a random “Miss Fire” for the lack of better term. I’ll randomly get what either feels like a momentary dead miss, or quick completely loss of power. A “skip” if you will. The frustrating part is that while I can typically get it to occur at partial throttle while highway cruising, It can happen at any time, any engine condition, and have a variable duration (it’ll miss once and be done, or it can do it for 15 miles straight). It does seem to do it more when ambient temps get above 80°F, but it’ll still do it when it is cooler outside as well.

I have data logged this thing to death looking for some sort of pattern and I have kept coming up empty handed. Whatever the issue is, the PCM does not appear to know about it. Or at least, it doesn’t know how to report it.

Lots of parts have been changed out while trying to chase this thing down. When you look at the list below, it’ll appear that I was just shot gunning parts at it, but there was a method to the madness and it actually created a better running motor, but the miss persists. So far the list of replaced parts is:

Fuel Pump (I have good fuel pressure)
Fuel Filter
Injectors
Plugs (2 times, with two different brands, same results)
Wires (2 times, with two different brands, same results)
Coil Packs
Cam Position Sensor
IAC
TPS
MAF
EGR solenoid
DPFE (and the hoses that go to it)
ERG cleaned and checked out good
No vacuum leaks to be found
Wiring harness appears to be in good shape as far as I can tell

When pulling plugs to inspect the cylinders, I’m not finding any irregularities. There isn’t a cylinder missing more than the others, and all the plugs look to be normal every time I pull them.

Compression is good and even across all the cylinders. I don’t recall what the numbers were off hand, but they were within spec according to the FSM I have.

So yeah, I’m completely stumped here after chasing this around for a long dang time. The only thing left to throw at it is a crank position sensor (crank pulley spins true by the way), but I have some serious doubts that’s going to fix it either at this point.

Searching around online shows that lots of Fords (including the V8 powered Exlopers) have random misfires that nobody seems to be able to find. This is a tad bid discouraging and I’m really hoping that I’m just missing something obvious here.

 

[gmanpaint]

You came to the right place to ask. There are a lot of technical guru's here that can throw out ideas and items to look into.

@Turdle might be able to point you in the right direction

 

[Turdle]

ECT ( engine coolant temp) sensor. I'd change this.
Also. disconnect and reconnect both main engine control harnesses, ( square o2 sensor fuel pump-trans harness right above intake manifold on firewall, and the PCM plug above the heater blower motor) look closely for pins out of line or slightly pushed back. A lot of intermittent issues are resolved by doing this.


If a misfire occurs from a dead or intermittent injector, a code will be set. however, in my experience once the spark charge hits ground the PCM has no way of knowing a misfire occurred. In other words, if it is ignition related you will not usually get a misfire code. I feel the issues is ignition related, however 2 sets of wires, plugs and coil-packs sure does have me scratching my head. Possibly a new crank sensor will help, pay real good attention to the connector also.
How about the coil-pack bracket. Is it nice and clean where the coils bolt on? this is their ground. Is your pcm ground strap in place? Coilpack connectors tight with both sides latched? ( those tabs break off real easy)

 

[Kage.]

ECT ( engine coolant temp) sensor. I'd change this.

Still original, but tests good and was verified with a mechanical gauge. I can put it on the list for considerations though.

Also. disconnect and reconnect both main engine control harnesses, ( square o2 sensor fuel pump-trans harness right above intake manifold on firewall, and the PCM plug above the heater blower motor) look closely for pins out of line or slightly pushed back. A lot of intermittent issues are resolved by doing this.

I gave the hairy eyeball to the PCM connections, and a quick glance at the other harness connection on the firewall. I'll take a closer look at it here soon.

If a misfire occurs from a dead or intermittent injector, a code will be set. however, in my experience once the spark charge hits ground the PCM has no way of knowing a misfire occurred. In other words, if it is ignition related you will not usually get a misfire code. I feel the issues is ignition related, however 2 sets of wires, plugs and coil-packs sure does have me scratching my head.

That's where my head keeps going (ignition) as well. since it feels more like the motor is shutting down briefly vs. just one dead cylinder. At one point it has acted like half of the coil packs went bad (like it was running on 4 cylinders). But it has only done that to me twice this year and I have yet to be able to recreate the condition that caused that. More confusion pointing towards the ignition I suppose.

Possibly a new crank sensor will help, pay real good attention to the connector also.

The connector is in good shape (And associated wiring) I pulled the timing cover off this winter to reseal that area up. It's been my experince with Hall sensors that they either work or they don't. Are the ones used on the 5.0's known for partially faling?

How about the coil-pack bracket. Is it nice and clean where the coils bolt on? this is their ground. Is your pcm ground strap in place? Coilpack connectors tight with both sides latched? ( those tabs break off real easy)

Coil brackets and connections are on there good. PCM Ground strap... hmm.. I'm trying to recall if this one had one. I honestly don't remember off hand if it does nor not..

Thanks for more leads!

 

[VR4]

I fought with an intermittent poor contact in the coil primary plug. Cleaned and tightened the pin just a bit and no issue since

 

[Dono]

I'm pushing all my chips to the middle of the table on injector related issue.

You have a injector connector/injector wiring issue. I had exactly the same issue with my 5.0.
What I finally found was that the injector connectors had been replaced in a previous life to me, and soldered with heat shrink tubing. Problem was, a sharp edge of one of the solder joints was poking thru just perfectly in to the other injector wire.

I also found the injector connectors get brittle and break up a bit, and no longer actually clip on to the injector.

While living this pain, I would at no time receive any engine codes to help me out. I even broke down and took it in to a shop to have them put the motor on a scope and use their years of experience to help diagnose. After a day of struggling with it, they returned my truck to me in the same condition scratching all their heads. Great, honest shop.

Maybe if you can get in there with one of those stethoscope dealies, you can listen to each injector fire. The problem is the intermittent nature of what you are experiencing. My symptoms were exactly like yours, and intermittent also. Remembering my aggravation is going to give me night mares tonight.

 

[boominXplorer]

I'll second wiring to an injector or ignition coil pack. You've changed out about every bolt on item it could be. How about the tone ring on the balancer? Any heavy spots of oxidation or damage?

 

[Kage.]

I fought with an intermittent poor contact in the coil primary plug. Cleaned and tightened the pin just a bit and no issue since

We seem to be in good shape there, but thanks for the suggestion.

I'm pushing all my chips to the middle of the table on injector related issue.

You have a injector connector/injector wiring issue. I had exactly the same issue with my 5.0.
What I finally found was that the injector connectors had been replaced in a previous life to me, and soldered with heat shrink tubing. Problem was, a sharp edge of one of the solder joints was poking thru just perfectly in to the other injector wire.

I also found the injector connectors get brittle and break up a bit, and no longer actually clip on to the injector.

While living this pain, I would at no time receive any engine codes to help me out. I even broke down and took it in to a shop to have them put the motor on a scope and use their years of experience to help diagnose. After a day of struggling with it, they returned my truck to me in the same condition scratching all their heads. Great, honest shop.

Maybe if you can get in there with one of those stethoscope dealies, you can listen to each injector fire. The problem is the intermittent nature of what you are experiencing. My symptoms were exactly like yours, and intermittent also. Remembering my aggravation is going to give me night mares tonight.

Our situation sounds extremely similar, and I agree, at this point I think I am dealing with a wiring issue internal to the harness (see below).

I'll second wiring to an injector or ignition coil pack. You've changed out about every bolt on item it could be. How about the tone ring on the balancer? Any heavy spots of oxidation or damage?

Leaning towards the harness at this poitn. Tone ring spins true and the balancer rubber is in good shape. No damage or oxidation that is notable.

So I Had some time Tuesday night to get after this the best that I could. I cleaned the firewall, PCM, Coil Pack, and Alternator connectors. I also gave the power distribution box a good once over. None of which showed any signs of corrision, and honestly the harness isn't brittle or falling apart even though it is 18 years old and has 185k miles worth of heat cycles on it.

However, the results of the above work reduced the amount and frequency that this thing misfires. So at this point, I believe that I am dealing with a wiring issue internal to the harness itself. Since I'm not finding any NOS harnesses, I'm left with tearing into this piece by piece (Boo!). But it is at least more derivable at this point.

I plan to start on the coil pack loom as I have time since it is a bit more accessible than the injector loom. And again, the injector loom looked pretty dang good when I swapped out the injectors.

I was kind of hoping everyone would say "Oh yeah, X tends to fail routinely causing your issue!". I'm actually surprised at how many comments about a bad engine loom there are for as new of a vehicle as this is.

I'll keep this thread updated as I find stuff out, but it'll be a while.

 

[Dono]

Yea, I wish we could have had an easy answer for you. Please remember to pop by and let us know how you are making out.

 

[delexploder]

I'm gonna throw my usual one in here , i had this issue for about a year with a 99 mountaineer , no code , ended up being a vacuum leak on the big nasty line that goes from the front drivers side of the upper intake to the evap under the battery , i found it by accident ,ran my hand down it looking for something else and it was cracked

 

[Kage.]

I'm gonna throw my usual one in here , i had this issue for about a year with a 99 mountaineer , no code , ended up being a vacuum leak on the big nasty line that goes from the front drivers side of the upper intake to the evap under the battery , i found it by accident ,ran my hand down it looking for something else and it was cracked

Funny you mention that. I had an odd idle issue after swapping the injectors out. Long story short, that same line you mentioned wound up being cracked, fixed that and the thing went back to idling like it should

 

[delexploder]

I agree with all the ideas here for possible causes but id look for simple things first

 

[97-5.0]

-Did you clean the maf sensor?
-add a dedicated ground wire to coil pack bracket.
-Use Ford plugs and wires! all else is garbage
-Ford primary o2 sensors, front 2
- confirm the crank sensor is clean on the end, not grease covered
- confirm tdc compression stroke and visually confirm cam position sensor magnet is intact and clean and reset with proper cam tool
- confirm exhaust manifolds are not leaking, vaccum on blow in tail pipe and feel around for leak

I'm in the same boat as you, finally running smoothly after replacing and touching everything under the hood,

Intermittent miss can be caused by almost anything

 

[97-5.0]

-Did you clean the maf sensor?
-add a dedicated ground wire to coil pack bracket.
-Use Ford plugs and wires! all else is garbage
-Ford primary o2 sensors, front 2
- confirm the crank sensor is clean on the end, not grease covered
- confirm tdc compression stroke and visually confirm cam position sensor magnet is intact and clean and reset with proper cam tool
- confirm exhaust manifolds are not leaking, vaccum on blow in tail pipe and feel around for leak

I'm in the same boat as you, finally running smoothly after replacing and touching everything under the hood,

Intermittent miss can be caused by almost anything

 

[97-5.0]

Won't hurt at all to blast wire harness and everything else under the hood with wd-40, spray at wire harness all around

How much Vaccum at idle in drive?
and in park?
And in park hold Rev at 3k rpm,

 

[Kage.]

Answers below in Red

-Did you clean the maf sensor? Cleaned and replaced it on a whim. No change.
-add a dedicated ground wire to coil pack bracket. Nope, I could do that.
-Use Ford plugs and wires! all else is garbage One Generic, now Ford OEM, no change, same with the plug wires.
-Ford primary o2 sensors, front 2 - Readings on these are fine, as long as the long term and short term fuel trims.
- confirm the crank sensor is clean on the end, not grease covered It is, and the harness/connector is good
- confirm tdc compression stroke and visually confirm cam position sensor magnet is intact and clean and reset with proper cam tool. I haven't actually pulled the replacement sensor apart recently. That's not a bad rabbit trail to follow.
- confirm exhaust manifolds are not leaking, vaccum on blow in tail pipe and feel around for leak Tight exhaust.

I'm in the same boat as you, finally running smoothly after replacing and touching everything under the hood, Yeah, I'm about 75% there. The thing runs dang good at this point, but the miss persists. See below.

Intermittent miss can be caused by almost anything That's no joke! I usually sell tings off if they have intermittent issues I can't track down, but I'm a bit deep in this one

Won't hurt at all to blast wire harness and everything else under the hood with wd-40, spray at wire harness all around

How much Vaccum at idle in drive?
and in park? Manual swap But it holds about 25 inches at idle
And in park hold Rev at 3k rpm, Haven't done this, but I can check it later.

So after farting around with the harness some the other day, the missfire got considerably better, but on the way home from work (and the way in this morning, the miss is back in frequency. So at this point I think being very systematic in going through the harness circuits is in my future. I will add an extra ground from the coil packs and take a peek at the CAM sensor as those two are pretty easy to knock out in a hurry.

Thanks!

 

[97-5.0]

25 inches at idle sounds a little high for a used engine, 19-21vaccum is more "normal" I believe??


Rev to 3k and hold will test if cats are plugged, vaccum should stay high, if not cats are bad

 

[Centaurus5.0]

Try wiggling your negative battery cable around while it's running and see it that does anything. A grounding kit is cheap and may help.

Cool front bumper!

 

[Kage.]

25 inches at idle sounds a little high for a used engine, 19-21vaccum is more "normal" I believe??


Rev to 3k and hold will test if cats are plugged, vaccum should stay high, if not cats are bad

Same vacuum at 3k as it is at idle (25-26 inches). I agree that the vacuum is a bit high for this high of a mileage motor, but both the PCM readings and what I see on a mechanical vacuum gauge agree. I will say that when I dropped the pan while doing the timing cover, the bottom end of the motor looked really dang good for its age.

Try wiggling your negative battery cable around while it's running and see it that does anything. A grounding kit is cheap and may help.

Cool front bumper!

Played around with the grounds and they're all looking pretty good. On a whim, I went ahead and added an extra ground for the coil packs (directly to the battery). No change from what I could tell:

Thanks on the bumper comment, I am pretty happy with how the front bumper turned out, I need to figure out something for the rear one of these days.

I did take it wheeling this past weekend, miss fired on the way down, miss fired on the way up, but it was happy as a clam all day on the trails. So yeah, still stumped at this point and the only thing I can figure to do is start tearing into the harness.

On the plus side, all of this work is having some benefits. Not only does the thing run smoother and pull harder than it ever has, I seem to be getting about 20-27% better fuel economy as well. Which sounds impressive until I tell you that it jumped up from 10mpg to 12 ish

 

[97-5.0]

Move that ground to the metal bracket the packs bolt too, at the front remove that black plastic clip and hook it there , remove the jumper between packs as not needed, bigger wire if possible and test again